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		<title>three.js webgl - math - orientation transform</title>
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			<a href="https://threejs.org" target="_blank" rel="noopener noreferrer">three.js</a> - gradually transform an orientation to a target orientation
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		<script type="importmap">
			{
				"imports": {
					"three": "../build/three.module.js",
					"three/addons/": "./jsm/"
				}
			}
		</script>

		<script type="module">

			import * as THREE from 'three';

			let camera, scene, renderer, mesh, target;

			const spherical = new THREE.Spherical();
			const rotationMatrix = new THREE.Matrix4();
			const targetQuaternion = new THREE.Quaternion();
			const clock = new THREE.Clock();
			const speed = 2;

			init();

			function init() {

				camera = new THREE.PerspectiveCamera( 70, window.innerWidth / window.innerHeight, 0.01, 10 );
				camera.position.z = 5;

				scene = new THREE.Scene();

				const geometry = new THREE.ConeGeometry( 0.1, 0.5, 8 );
				geometry.rotateX( Math.PI * 0.5 );
				const material = new THREE.MeshNormalMaterial();

				mesh = new THREE.Mesh( geometry, material );
				scene.add( mesh );

				//

				const targetGeometry = new THREE.SphereGeometry( 0.05 );
				const targetMaterial = new THREE.MeshBasicMaterial( { color: 0xff0000 } );
				target = new THREE.Mesh( targetGeometry, targetMaterial );
				scene.add( target );

				//

				const sphereGeometry = new THREE.SphereGeometry( 2, 32, 32 );
				const sphereMaterial = new THREE.MeshBasicMaterial( { color: 0xcccccc, wireframe: true, transparent: true, opacity: 0.3 } );
				const sphere = new THREE.Mesh( sphereGeometry, sphereMaterial );
				scene.add( sphere );

				//

				renderer = new THREE.WebGLRenderer( { antialias: true } );
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( window.innerWidth, window.innerHeight );
				renderer.setAnimationLoop( animate );
				document.body.appendChild( renderer.domElement );

				//

				window.addEventListener( 'resize', onWindowResize );

				//

				generateTarget();

			}

			function onWindowResize() {

				camera.aspect = window.innerWidth / window.innerHeight;
				camera.updateProjectionMatrix();

				renderer.setSize( window.innerWidth, window.innerHeight );

			}

			function animate() {

				const delta = clock.getDelta();

				if ( ! mesh.quaternion.equals( targetQuaternion ) ) {

					const step = speed * delta;
					mesh.quaternion.rotateTowards( targetQuaternion, step );

				}

				renderer.render( scene, camera );

			}

			function generateTarget() {

				// generate a random point on a sphere

				spherical.theta = Math.random() * Math.PI * 2;
				spherical.phi = Math.acos( ( 2 * Math.random() ) - 1 );
				spherical.radius = 2;

				target.position.setFromSpherical( spherical );

				// compute target rotation

				rotationMatrix.lookAt( target.position, mesh.position, mesh.up );
				targetQuaternion.setFromRotationMatrix( rotationMatrix );

				setTimeout( generateTarget, 2000 );

			}

	</script>

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